Secrecy system



W. J. ZENNER SECRECY SYSTEM April 3, 1951 5 Sheets-Sheet l Filed June 23, 1949 NVENTOR CIPHER April 3, 1951 W, J, zENNl-:R 2,547,515

sEcREcY SYSTEM Filed June 23, 1949 3 Sheets-Sheet 2 FIG. 2

INVENTOR WALTER J. ZENNER ATTORNEY April 3, 1951 w. J. ZENNER 2,547,55

sEcREcY SYSTEM Filed June 25, 1949 s sheets-sheet s INVENTOR FIG. 3

WALTER J. ZENNER BY Wauw ATTORNEY Patented Apr. 3, 1951 UNITED STT ES GFFIC SECRECY SYSTEM Walter J. Zenner, Des Plaines, Ill., assigner to Teletype Corporation, Chicago, Ill., a corporation of Delaware This invention relates to secret communication systems and more particularly toA secret printing telegraphv systems. Still more particularly the invention deals with an arrangement. for communicating information in either plain or enciphered form.

The present invention contemplates the use of a ciphering maze of the type shown in either of the United StateszPatents 1,861,857 and 1,510,441 issued to E. H.. Hebern. The maze may `consist of any number of code wheels, each. of which will be wired dierently. The more code wheels utilized' in the ciphering maze, the: greater the. security; however, the actual number of code wheels in the ciphering maze is immaterial for the purposes of the present invention. Besides the' fact. that each code wheel is wired: differently, each is also wired so that there will be no signal reversals. In some ciphering systems, for example, when a particular character such as the letter A is enciphered, the corresponding enciphered character might be the letter Y and the coding apparatus is such that the letter Y willY be enciphered as the letter A This type of a system renders the apparatus more simple but has the disadvantage of also facilitating the breaking of the cipher. The maze contemplated for use in the present invention might encipher the letter A `as the letter Y however, itv would only be a random coincidence that the letter "Y would be enciphered as the letter A by the same settings of the code wheels. Therefore, it is apparent that in order to decipher enciphered signals it is not only necessary that the code. wheels occupy the same settings for both operations, but also that, in the deciphering operation, the signals pass through the ciphering maze in a direction opposite to that for the enciphering operation.

Accordingly, a principal object of the present invention is to provide means for causing the signals to pass through the ciphering maze in opposite directions for deciphering and enciphering operations.

Another object of the present invention is to provide a secrecy system wherein messages are normally handled in Aan enciphered condition but which may be handled in plain text or clear condition so long as the operator maintains a special key or switch depressed.

A further object of the present invention is to provide a system in which each station is in condition normally for receiving messages, but which, upon the actuation of a transmitter thereat, is automatically placed in transmitting condition.

In the present invention a manuallyI operable push button switch, upon actuation, is designed to. control six contact swingers. QI poles in unison. In one positionl of the push button all the poles are in plain text position, whereas all ot the poles are in cipher position: when the push button occupies its other position. When the system is. in plain text conditionV the linecircuit extends directly through the local receiver and transmitter to thereby enable transmission and reception in the clear.

When it is desired to carry on communications in cipher the switch is placed in cipherv position. As a result the line circuit no longer ex.- tends directly through the local printer and transmitter, and the incoming Signals are directed instead through a receiverinv the ciphering unit and thence to an outgoing; line to complete the line circuit. These signals are deciphered by the ciphering unit :and transmitted in plain tex condition by a transmitter asso.- cated with the ciphering unit to the local printer. The ciphering unit is normally in condition. for receiving enciphered signals from the line and for deciphering these signals for retransmission in plain text to the local printer. When itA is desired to transmit enciphered signals over the. outgoing line from the local transmitter, such signals are transmitted in plain text to the receiver in the ciphering unit. Anextra cam on the local transmitter cam, shaft is designed to cause the opening of four contacts and closurey of ve contacts during transmission by the local transmitter. The fth of these contacts is in circuit with a pair of reversing relays and cau/ses the circuits through the ciphering maze to be reversed so as to enable enciphering of signals from plain text to ciphen The rmainder of the contacts, upon actuation, place the transmitter associated with the ciphering unit in the line; circuit and the ciphering unit receiver in the local circuit.

In addition to the objects above enumerated other objects and advantages of the invention will be apparent from the following detailed description when read in conjunction with the apiizended drawings wherein:

Figs. 1, 2, and 3 represent :a schematic View of the invention;

Fig. 4 shows how Figs. 1, 2, and 3 should be arranged; and

Fig. 5 is a schematic view of a loop circuit inl which the present invention is applicable.

It is to be borne in mind that the: drawings show the apparatus at but a single station, it being considered unnecessary to show or describe more than a single station inasmuch as all stations on the circuit are identical. The circuit in which all stations are connected is of the type commonly known as a loop circuit represented by reference numeral 9 in Fig. 5; that is, all stations I6 are in series with one another, with each station having what is conveniently referred to as an incoming line and an outgoing line.

With reference to Figs. l, 2, and 3 of the drawings reference numeral II represents a local printing receiver of any well known type and reference numeral I2 designates a transmitter, preferably of the keyboard type, but of any well known design. Reference numeral I3 designates a selective control unit of the type disclosed in the copending application for patent of W. J. Zenner Serial No. 739,747, led April 7, 1947. For a detailed description of this selective control unit I3, reference should be made to this application of W. J. Zenner which is hereby incorporated into and made a part of the present specification by reference. A ciphering unit is represented schematically and generally by reference numeral I4, the ciphering unit I4 however being deemed to include the selective control unit or receiver I3 as well as a transmitting distributor represented generally by reference numeral I6. It is to be understood that these units are referred to as specific vtypes of units simply for convenience and it is contemplated that other units capable of performing the functions could be used without departing from the spirit or scope of the invention.`

lA six pole double throw spring return push button switch I7, having poles I8, I9, 2|, and 22, is normally retained in its downward or cipher position by means of a compression spring 25. With the switch |7 in its cipher position its poles I8, I9, 2|, and 22 engage contact points 23, 24, 26, and 27 respectively. When the switch I7 is moved upwardly to its plain text position, the poles I8, I9, 2|, and 22 engage contact points 28, 26, 3 I, and 32 respectively.

The transmitter I2 has a transmitting cam .'w,

shaft 33 on which is mounted the usual stop cam 34 and ve transmitting cams 36. When no signals are being transmitted by the transmitter I2 the stop cam 34 retains its contact 37 closed against a contact bar 36.l of signals by the transmitter I2 the cams 36 close their contacts 39 sequentially and permutatably according to the signals to be transmitted.

VWhen it is desired to transmit and receive in clear or plain text the switch I7 is moved upwardly causing4 the closure of the poles I3, I9, 2|, and 22 respectively with the contacts 2'8, 2'9, 3|, and 32.' Under this condition a circuit is established fro-m the incoming line over the pole 2|, through the contact points 3| and 23, through the pole I9, over a lead 4I, through a selector magnet 42 in the receiver I I, over a lead 43,"through either the contacts 37 or 36, through the contact bar 3B, over a lead 44, through the pole I8 and contact 28, over a lead 46, through the4 contact 32 and pole 22,.to the outgoing line. Under this condition incoming signals are received in plain text condition by the selector magnet 42, the circuit through the transmitter I2 passing through the stop contact 37.r When the transmitter I2 operates under this condition the circuit obviously is through the selector magnet 42 and the locally generated signals are therefore printed by the receiver I I.

l A cam 47 secured to and rotatable with the During transmission shaft 33 has a high portion 48 which oscillates a follower 49 as the shaft 33 rotates. The follower 49 has five poles 5I, 52, 53, 54, and 56 which, when moved to the right, as shown, occupy their receiving position, the poles 5| 52, 53, and 54 respectively engaging contacts 57, 58, 59, and 6| under this condition. As the shaft 33 rotates during the transmission of a signal by the transmitter I2, so as to permit the follower 49 to go oi of the high portion 48 of the cam 47, the follower 49, and its poles 5I, 52, 53, 54, and 56 move to the left and thereby engage respectively the contacts 62, 63, 64, 66, and 67.

Two poles |66 and |67 are also operable with the switch I7 in the same manner as the poles IIS-22. Whenrthe switch I7 occupies its upper position, that is, when transmission and reception is being handled in clear a circuit extends from battery |68 through a Contact |66, over the pole |66, over a lead I7I, through a selector magnet 7| in the selective controlunit I3, over a vlead |72, through the pole |67, through a contact |73, to the battery. Thus battery is maintained on the selector magnet 7| continuously during clear transmission.

When signals are being received in cipher,` while the switch I7 occupies the position shown, they pass over a circuit from the incoming line, over the pole 2|, through the contact 26, over a lead 68, through the closed contact 57 and pole 5|, over a lead 66, through a contact |74 and the pole |66, over the lead |7I, through the selectoi magnet 7| in the selective control unit I3, over a lead |72, through the pole |67 and a contact, over a lead 72, throughV the closed pole 53 and contact 59, over a lead 73, through the closed contact 27 and pole 22, to the outgoing line. When signals are being transmitted by the transmitter I2 under cipher conditions the signals generated thereby are also impressed upon the selector magnet 7| in the selective control unit I3. During the generation of signals by the transmitter I2 it will be noted that the follower 46 moves off the peak 48 to the low portion of the cam 47 while the contacts 39 close sequentially and permutatably against the contact bar 38, and therefore the poles 5I, 52, 53, 54, and 56 respectively engage the contacts 62, 63, 64, 66, and 67. The path taken by the generated signals extends from the transmitter I2, over the lead 44, through theclosed pole I 8 and Contact 23, over alead 74, through a battery 76, over a lead 77, through the closed contact 64 and pole 53, over the lead 72, through the contact |76 and pole |67, over the lead |72, through the selector magnet 7|, over the lead |7I, through the pole |66 and contact |74, over the lead 68,'through the closed pole 5I and contact 62, over a lead 76, through the closed contact 24 and po-le I9, over the lead 4I, through the selector magnet 42 in the printing receiver I I, over the lead 43, to the transmitter I2. Thus the transmitted signals are received and printed by the local receiver II in plain text.

When signals are being transmitted by the transmitter I2, under cipher conditions, upon closure of the pole 56 with the contact 67, an energizing circuit for a pair of direction relays 79 and 8| is established from the battery 76, over the lead 77, through the closed contact 67 and pole 56, over a lead 82, vthrough the direction relay 8|, over a lead 83, through the direction relay 73, over a lead 84 to the battery 76. Upon energization the relays 79 and 8| pull down all of their armatures 86 and 3l respectively to make With the front contacts 88 and 8S respectively.

When the signals, transmitted from the transmitter |2, are received by the selector magnet 1|, a Contact pair 9|, in the selective control unit, corresponding to the transmitted signal, and a universal contact pair 92 are closed. Upon closure of the contacts Si and 92 a universal contact 95 momentarily closes. The universal contact .pair S2, upon closure, completes an energizing circuit for a stepping magnet 93 of the cipher-ing unit I4, from positive battery, through the closed universal contact pair 92, over a lead 94, through the stepping magnet S3, over a lead 96, over a lead Si, through a start magnet 98 of the transmitting distributor I6, to negative battery.

It should be noted at this point that during clear transmission battery is maintained on the selector magnet 1| continuously and under this condition the universal contact 92 does not close so that the stepping magnet 93 does not step the maze I4 under this condition. Closure of one of the contact pairs 9| at this time completes a circuit from positive battery, through the momentarily closed contact pair 95, over a lead S2, through the selectively closed contact pair 8|, over the proper one of a group of leads 32, through the corresponding armature 8B and contact 3S (remembering that the armatures 85 and 8l engage contacts 88 and 3.9 respectively at this time), over the corresponding lead of a group of leads HEI, over the corresponding lead |22, through a maze ID3 like that shown in the afore-nentioned patents to E. H. Hebern, over the proper one of a group of leads |64, over one of a group of leads |95, through the proper ones of the iront contacts B9 and armatures 81, over the corresponding one of a group of leads |21, through a corresponding one of a .plurality of relays m8, over the lead 31, through the start magnet 98, to negative battery. Whichever one of the relays |23 is energized in response to the closure of one of the contact pairs 9| pulls up all oi its associated armatures. rhe armatures associated With each of the relays |98 consist of a locking armature |89 and up to iive signal impulse armatures ||2, ||3, H4, and H5. When the associated locking armature |35 is pulled up by any of the relays |33 a locking circuit is established for such relay from positive battery, over an inner ring Il? in the transmitter distributor |5, through a pair of connected brushes H8 and H9 which cooperate respectively with the ring ill and a ring segment |2|, through the ring segment |2l, over a lead |22, through the pulled up locking armature |09 and its associated` contact |23, through the previously energized relay |23, over the lead 9i, through the start magnet Q3, to negative battery.

When the start magnet 98 is energized, an arm |24 of the transmitting distributor I6 carrying the lbrushes ||8 and H9 commences rotating in a clockwise direction. The initial energizing circuit for the relays |38 is of suicient duration to retain the selected one of these relays energized until the arm |24 rotates suiciently to bring the brush H9, into engagement With the ring segment |2| and thereafter the aforementioned locking circuit for the relays |98 becomes effective until the brush |9 moves off of the segment |2|. The arm |24 also carries another pair of brushes |25 and |2'|, the brush |2'| being designed for engaginga ring |28 and the brush |26 being designed for engaging a start segment |29, a, group of iive signal impulse segments |3.|., |32, |33, |34, and |35, and a stop segment |311. A lead |38 connects the No. 1 impulse segment |3.| With a plurality of leads |39, each of which is connected With a contact |4| designed to be engaged by the No. l impulse armature |||v when the corresponding relay |08 becomes energized. The No. 2 impulse segment |32 is connected to each of the contacts |42 which are cooperablewith the armatures ||2, by means of alead' |43 and a group of leads |44. Contacts |46 associated with armatures ||3 are connected tothe No. 3` impulse segment |33 by means of leads |41 and |48, contacts |49 associated with armatures H4 are connected to the No. 4 impulse segment |35 by means of leads |5| and |52, and contacts |53 associated with armatures ||5 are con-v nected to the No. 5 impulse segment |35 by means of leads |54 and |56.

As the arm |24 rotates, permutation signais are generated, in accordance with Whichever relay 8 is energized, and impressed on the loop circuit over a circuit extending from the incoming line, through the closed pole 2| and contact 25, over the lead @8, through the closed contact |53 and pole 52, over a lead |57, over a lead |58, through Whichever permutation of armatures l5 are closed with their corresponding contacts |4|, |42, |46, |49, and |53, over a corresponding permutation of leads |33, |44, |47, |54, and |53, over a corresponding permutation of leads |38, |43, |48, |52, and |56, through a corresponding permutation of the signal impulse segments |3|, |32, |33,l |34, and |35, through the brushes |2 and |27', through the ring |28, over a lead |53, through the pole 54 and contact 66 (closed at this time), over the lead |3, through I the closed Contact 2l and pole 22, to the outgoing line. When the arm |24 rotates beyond the No. 5 impulse segment |35 the 4brush ||9 rotates oil of thev ring segment |2| and thus the locking circuit for the selected relay |33 is broken. At this time if another signal is transmitted from the transmitter kl2 the brush |23, since it engages the stop segment |3'|, thereby applies a marking or current condition on the loop circuit until the start magnet 58 is again energizedl by the next signal impressed to the relays |28, over a circuit extending from the incoming line, through the closed pole 2| and contact 2t, over the lead S8, through the closed contact S3 and pole 52 (closed at this time because the transmitter l2. is trans-v mitting another signal), over the lead |57, over the lead |53, through the stop segment |3'|, through the brushes l2?,i and |27, through the ring |28, over the lead |59, through the closed pole 54 and contact et, over the lead i3, through the closed contact 2 and pole 22, to the outgoing line.

If the transmitter has no further signals to be transmitted, continuous marking is maintained on the loop circuit over a circuit from the incoming line, through the closed pole 2| and contact 2h, over the lead 68, over the closed contact 5'? and pole 5|, over the lead 69, over the contact |74 and pole I, over the lead through the selector magnet il in the selective control unit I3, over the lead |'|2, through the pole |61 and contact H6, over the lead l2, through the closed pole 53 and contact 53, over the'lead '53, through the closed contact 2l and pole 22, to the outgoing line.

From the above description of a transmitting operation under cipher conditions it is apparent that the signals are generated'in clear by the transmitter I2, printed in clear by the local receiver I I, and impressed in clear to the selector magnet 1I of the sequence selector unit I3. In response Yto each signal a selected contact 9| and universal contacts 92 and 95 are closed. The closure of the universal contact 92 completes a circuit to the .stepping magnet 93 of the maze I4 whereas closure of the selected contact 9| and the universal contact 95 completes a circuit through the maze I4 and energizes one of the relays I 88 representing an enciphered signal corresponding to the clear signal transmitted by the transmitter I2. The energized relay |88 pulls up its armatures and by means of the transmitter distributor the enciphered signal is converted to a permutation signal Which is transmitted over the loop circuit 9.

It, of course, is to be borne in mind, even though only a few contacts 9|, armatures 86 and 81, and relays |88 are shown, that since a ve unit code is being used in the invention, there will be thirty-two of each of these contacts, armatures, and relays. Of course if a six or more unit code were used, which it is contemplated Will be used when necessary, the contacts, armatures, and relays would accordingly be increased.

In the case Where enciphered signals are received at the local station it is necessary that they be deciphered before being impressed to the local receiver selector magnet 42. Under these conditions the transmitter cam shaft 33 is stationary in the position shown in Fig. 1, with the follower 49 on the high portion 48 of the cam 41 and the poles 5|-56 occupying their rightward positions as shown. In such case the received signals follow a circuit from the incoming line, through the pole 2| and contact 2B, over the lead 58, through the contact 51 and pole 5|, over the lead 69, through the contact |14 and pole |86, over the lead |1I, through the selector magnet 1I, over the lead |12, through the pole |51 and contact |15, over the lead 12, through the pole 53 and contact 59, over the lead 13, through the closed contact 21 and pole 22, to the outgoing line. It will be noted that under these conditions the pole 56 and contact 51 are not closed and therefore the direction or reversing relays 19 and 8| are not energized, and accordingly the armatures 85 and 81 occupy their upward position in engagement respectively with the contacts I5! and |62.

As in the case when the transmitter I2 is transmitting, the received signals impressed to the selector magnet 1| cause the selective closure of one of the contacts 9| and the invariable closure of the universal contact 92 and the universal momentarily closable Contact S5. Closure of the Contact Q2 enables the energization of the stepping magnet 93 as already described.

Closure of one of the contacts 5I at this time completes a circuit from positive battery through the momentarily closed contact 55, over the lead 33, through the selected contact 9 I, over the lead 99 connected to the selected contact 9|, through the corresponding armature 86 and Contact IBI, over the corresponding lead |54, over the path through the code Wheels of the maze |53, over the lead |532 determined by the settings of the maze code wheels, through the corresponding contact |62 and armature 81, over the corresponding lead |51, through the corresponding relay I Qt, over the lead 81, through the transmitter distributor start magnet 98, to negative battery.4 It will be noted that the received signals passed through the maze |03 in a rightward direction and during such passage enciphered signals have been deciphered Whereas, as it willl be recalled, during the enciphering operation of clear signals they passed through the maz |83 in a leftward direction, in each case the circuits having been traced from one of the selective contacts 9| to the selected one of the relays IIIB. Therefore, the selected relay |08 corresponds to a clear signal when the local station is receiving under cipher conditions. Upon the selection of the relay |08 it pulls up all of its armatures, Vincluding its locking armature |59 and its code armatures III--I I5. The code armatures III-H5 and their cooperative contacts, upon closure, are in circuit respectively with the signal impulse segments |3|-|35.

When the arm |24 rotates in response to the energization of the transmitter distributor start magnet 98 a transmitting circuit is established for impressing the deciphered signal to the local receiver I I over a circuit from the ring |28, over the lead |59, through the closed pole 54 and contact 5|, over the lead 11, through the battery 16, over the lead 14, through the closed contact 23 and pole I8, over the lead 44, through the closed contact bar 35 and stop contact 31, over the lead 44, through the selector magnet 42 in the receiver II, over the lead 4|, through the closed pole I9 and contact 24, over the lead 18, through the closed contact 58 and pole 52, over the lead |51, over the lead I 53, through the closed permutation or armatures III-IIS and contacts I4I, |42, |48, |49, and |53, over the corresponding permutation of leads |39, |44, |41, I 5| and |54, over the corresponding permutation of leads |38, |43, |48, |52, and |56, through the corresponding permutation of signal impulse segments |3|-|35, through the brushes |26 and |21, to the ring |28. When the arm |24 has rotated through a complete revolution and returned to its stop position (as shown) with the brush |26 on the stop segment |31 and with the brush H9 off of the segment I2I, the locking circuit for the selected relay |08 is broken and all of its armatures fall away. AtV

this time, until another signal is impressed to one of the relays |58, a marking or energized condition of the local selector magnet 42 is maintained by means of a circuit extending from the ring |28, over the lead |59, through the closed pole 54 and Contact 6|, over the lead 11, through the battery 18, over the lead 14, through the closed contact 23 and pole I8, over the lead 44, through the closed contact bar 35 and contact 31, over the lead 43, through the selector magnet 42, over the lead 4I, through the closed pole i3 and Contact 24, over the lead 18, through the closed contact 58 and pole 52, over the lead |51, over the lead |58, through the stop segment |31, through brushes |26 and |24, to the ring |23.

It is therefore apparent that incoming enciphered signals from a distant station are first impressed to the selector magnet 1| in the selective control unit I3. The selective control unit I3, in response, causes one of a plurality of contacts to be selectively closed to thereby complete a circuit through the maze |83 and to a relay |98 which corresponds to the clear signal deciphered by the maze |03. The clear signal impressed on the relay I 88 is then converted to a five unit permutation signal and transmitted by the transmitter distributor I6 over a circuit to the local receiving printer I.

i By the present invention there is provided Aa ciphering system which is designed to handle enciphered transmission whereby a ciphering unit at a particular station normally functions to decipher incoming signals, -but which is automatically rendered effective to encipher' transmitted signals. By the slight manual operation of depressing a key, transmission in the clear is made possible. It is contemplated that the settingsof the code wheel-s in the ciphering maze at the different stations will be uniform and will be accomplished by any of the methods well known at the present time.

Various changes and modications may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In a secret printing telegraph system, a line, a plurality of stations on said line, a ciphering maze at each of said stations, each ciphering maze eiiective for deciphering received signals in one direction therethrough and enciphering transmitted signals in the opposite direction therethrough, each of said ciphering mazes being in condition normally for deciphering received signals, means at each station operable automatically upon the transmission of a signal therefrom for causing said ciphering maze to encipher said signal, and means operable automatically upon the encipherment of said signal for transmitting the enciphered signal over said line.

2. In a secret printing telegraph system, a line, a plurality of stations on said line, a ciphering maze at each of said stations, each ciphering maze effective for deciphering received signals in one direction therethrough and enciphering transmitted signals in the opposite direction therethrough, each of said ciphering mazes being in condition normally for deciphering received signals, a transmitter at each of said stations for generating plain text signals, means at each station effective automatically upon the generation of a plain text signal by said transmitter for causing said ciphering maze to encipher said signal, and means operable automatically upon the encipherment of said signal for transmitting the enciphered signal over said line.

3. In a secret printing telegraph, system, a line, a plurality of stations on said line, ciphering means at each of said stations for deciphering received signals and enciphering transmitte signals, said ciphering means being effective to decipher signals passing therethrough in one direction and to encipher signals passing therethrough in the opposite direction, means associated with each of said ciphering means for controlling the direction of the passage of signals through said ciphering means, and normally eifective to cause passage of signals through said ciphering means in said rst mentioned direction to thereby cause decipherment of signals, a transmitter at each of said stations for generating plain text signals, means at each station effective automatically upon the generation of a plain text signal for causing said direction control means to cause the signal to pass through said ciphering means in said second mentioned direction to thereby cause encipherment of said signal, and means operable automatically upon the encipherment of said signal for transmitting the enciphered signal over said line.

4. In a secret printing telegraph system, a line,

a plurality of stations on said line, a ciphering maze at each of said stations, veach ciphering maze eective for deciphering received signals in one direction therethrough and enciphering transmitted signals in the opposite direction therethrough, said ciphering maze 'being normally effective to decipher received signals, cipher controlling means -for rendering s'ai'd ciphering maze ineffective to decipher received signals and eective to encipher transmitted signals, means at each station for generating plain text signals, means at each station effective automatically upon the generation of a plain tex-t signal for causing said cipher controlling means to render said ciphering maze ineifective to decipher received signals and effective to encipher said plain text signal, and means operable automatically upon the encipherment of said signal for transmitting the enciphered signal over said line.

5. In a secret printing telegraph system, a line, a plurality of stations on said line, a ciphering maze at each of said stations, each ciphering maze effective for deciphering received signals in one direction therethrough and enciphering transmitted signals in the opposite direction, therethrough, said ciphering maze being normally effective to decipher received signals, relay means for rendering said ciphering maze ineffective to decipher received signals and effective to encipher transmitted signals, means at each station for generating plain text signals, a cam rcontrolled switch at each station effective automatically upon the generation of a plain text signal for causing said relay means to render said ciphering maze ineifective to decipher received signals and eifective to encipher said plain text signal, and means operable automatically upon the encipherment of said signal for transmitting the enciphered signal over said line.

6. Ina secret printing telegraph system, a line, a plurality of stations on said line, a ciphering maze at each of said stations effective to decipher signals passing through said maze in a first direction and effective to encipher signals passing through said maze in an opposite direction, relay means at each station for controlling the direction of the passage of signals through said maze, said relay means normally enabling signals to pass through said maze in said first direction to cause deciphering, a transmitter at each of said stations for generating plain text signals, a cam controlled switching means at each station eifective automatically upon the generation of a plain text signal by said transmitter for actuating said relay means to cause the signal to pass through said maze in said opposite direction, whereby said signal is enciphered, and means operable automatically upon the `encipherment of said signal for transmitting the enciphered signal over said line.

7. In a secret printing telegraph system, a line, a plurality of stations on said line, a transmitter at each of said stations for generating plain text signals, a receiver at each of said stations, a ciphering maze at each of said stations, each ciphering maze eiective for deciphering enciphered signals in one direction therethrough and for enciphering plain text signals in the opposite direction therethrough, a selective control unit associated with each ciphering maze for receiving plain text signals generated by the transmitter at the same station and for receiving enciphered signals from another station.

and for directing both of these types of signals to the ciphering maze associated therewith, relay means at each station normally eiective to cause said ciphering maze at the same station to decipher enciphered signals received by the 5 selective'control unit thereat, means at each sta,- tion actuated by said transmitter at the same station upon the generation of a plain text signal thereby for operating said relay means at the same station to cause the ciphering maze to encipher said plain text signal upon its receipt by the selective control unit at the same station, and means operable automatically upon the encipherment of said plain text signal for trans- 12 mitting the corresponding encphered signal over said line to the other stations thereon.

WALTER J. ZENNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS m Number Name Date 1,310,719 Vernam July 22, 1919 1,522,775 Friedman Jan. 13, 1925 2,405,569 Fitch et al Aug. 13, 1946 2,406,829 I-Iaglund et al. Sept. 3, 1946 

